Answer for number b
not for a or c

Between the integers 5,000 and 5,500

1 mi x (5,280 ft/1 mi) x (1 yd/3 ft) = ?? 
Note that the first factor cancels miles and changes miles to feet, the second factor cancels feet and converts to yards. The idea here is to place the factors such that the unit you don't want cancels and the unit you want is the only one left. I hope this helps.